Next-generation semiconductor memory devices (e.g., a ferroelectrie random access memory (FRAM), a magnetic random access memory (MRAM), a phase-change random access memory (PRAM), and so forth) are being developed to meet increasing demands for high performance and low power consumption of semiconductor memory devices. In the next-generation semiconductor memory devices, a memory element may be formed of a non-volatile and variable resistance material. In other words, the memory element may exhibit an electric resistance that can be selectively changed depending on a current or voltage applied thereto and can be preserved even when a current or voltage is not supplied.
PRAMs are of particular interest because they have the potential for high operation speed and high integration density. Accordingly, intensive research is being performed in the area of PRAM device.